Received-SPF: pass (google.com: domain of linux-kernel+bounces-106619-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45e3:2400::1 as permitted sender) client-ip=2604:1380:45e3:2400::1;
Precedence: bulk
MIME-Version: 1.0
References: <000000000000bbb3d80613f243a6@google.com> <CAKEwX=MAX0km1p43DQmKbeSy2G4dPFHiF+deH_qzqygc2Vnjig@mail.gmail.com>
In-Reply-To: <CAKEwX=MAX0km1p43DQmKbeSy2G4dPFHiF+deH_qzqygc2Vnjig@mail.gmail.com>
From: Yosry Ahmed <yosryahmed@google.com>
Date: Mon, 18 Mar 2024 13:17:19 -0700
Message-ID: <CAJD7tkbEuFkGuQeYjKS02rQoAAKOKieAJ1P2mwukirW3e2JN9A@mail.gmail.com>
Subject: Re: [syzbot] [mm?] kernel BUG in sg_init_one
To: Nhat Pham <nphamcs@gmail.com>
Cc: syzbot <syzbot+adbc983a1588b7805de3@syzkaller.appspotmail.com>, 
	akpm@linux-foundation.org, chengming.zhou@linux.dev, hannes@cmpxchg.org, 
	linux-kernel@vger.kernel.org, linux-mm@kvack.org, 
	syzkaller-bugs@googlegroups.com, Barry Song <v-songbaohua@oppo.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Mon, Mar 18, 2024 at 11:00=E2=80=AFAM Nhat Pham <nphamcs@gmail.com> wrot=
e:
>
> On Mon, Mar 18, 2024 at 9:58=E2=80=AFAM syzbot
> <syzbot+adbc983a1588b7805de3@syzkaller.appspotmail.com> wrote:
> >
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    e5eb28f6d1af Merge tag 'mm-nonmm-stable-2024-03-14-09-3=
6' ..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=3D13043abe180=
000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=3D19bb57c23df=
fc38e
> > dashboard link: https://syzkaller.appspot.com/bug?extid=3Dadbc983a1588b=
7805de3
> > compiler:       arm-linux-gnueabi-gcc (Debian 12.2.0-14) 12.2.0, GNU ld=
 (GNU Binutils for Debian) 2.40
> > userspace arch: arm
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=3D1706d2311=
80000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=3D13ba7959180=
000
> >
> > Downloadable assets:
> > disk image (non-bootable): https://storage.googleapis.com/syzbot-assets=
/8ead8862021c/non_bootable_disk-e5eb28f6.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/0a7371c63ff2/vmli=
nux-e5eb28f6.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/7539441b4add=
/zImage-e5eb28f6.xz
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the co=
mmit:
> > Reported-by: syzbot+adbc983a1588b7805de3@syzkaller.appspotmail.com
> >
> > ------------[ cut here ]------------
> > kernel BUG at include/linux/scatterlist.h:187!
>
> Looks like the provided buffer is invalid:
>
> #ifdef CONFIG_DEBUG_SG
> BUG_ON(!virt_addr_valid(buf));
> #endif
>
> which is "src" from:
>
> sg_init_one(&input, src, entry->length);
>
> Looking at the surrounding code and recent history, there's this
> commit that stands out:
>
> mm/zswap: remove the memcpy if acomp is not sleepable
> (sha: 270700dd06ca41a4779c19eb46608f076bb7d40e)
>
> which has the effect of, IIUC, using the zpool mapped memory directly
> as src, instead of acomp_ctx->buffer (which was previously the case,
> as zsmalloc was not sleepable).
>
> This might not necessarily be a bug with that commit itself, but might
> have revealed another bug elsewhere.
>
> Anyway, cc-ing the author, Barry Song, to fact check me :) Will take a
> closer look later.

I am not a highmem expert, but the reproducer has CONFIG_HIGHMEM=3Dy,
and it seems like zs_map_object() may return a highmem address if the
compressed object is entirely in a single page to avoid copying to a
buffer:

if (off + class->size <=3D PAGE_SIZE) {
   /* this object is contained entirely within a page */
   area->vm_addr =3D kmap_atomic(page);
   ret =3D area->vm_addr + off;
   goto out;
}

The virt_addr_valid() check seems to indicate that we expect a direct
map address in sg_init_one(), right?